[ty] reveal_type diagnostics in unreachable code

[sharkdp]

Summary

In unreachable sections of code, we infer Never for symbols that were define outside the unreachable part. This means, that we infer Never for the reveal_type symbol here:

from typing import reveal_type

if False:
    reveal_type(1)  # no diagnostic! `reveal_type` is inferred as `Never`

This PR fixes that by explicitly detecting callables named reveal_type that have a type of Never. I'm sure there ways to make this more bullet-proof, but it seems very unlikely that this will cause "false positives".

I'm not sure if we should do something similar assert_type/assert_never, but it seems to me like those are different. Instead of just revealing a potentially surprising type in unreachable code, those could accidentally look like they succeed when they shouldn't, or they could fail when they should appear to succeed.

Test Plan

New Markdown tests.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 85.29%. The percentage of expected errors that received a diagnostic held steady at 78.13%. The number of fully passing files held steady at 64/132.

[astral-sh-bot]

Memory usage report

Memory usage unchanged ✅

[astral-sh-bot]

ecosystem-analyzer results

Lint rule	Added	Removed	Changed
invalid-await	0	40	0
invalid-return-type	0	1	0
Total	0	41	0

Changes in flaky projects detected. Raw diff output excludes flaky projects; see the HTML report for details.

Full report with detailed diff (timing results)

[AlexWaygood]

This looks great to me. I do think we need to do something about assert_type diagnostics in unreachable code -- see #24024 (comment) -- but we can discuss that separately